<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<title></title>
</head>
<body>
<p class="p1 p">p1</p>
<p class="p2 p">p2</p>
<p class="p3 pp">p3</p>
<script type="text/javascript">
	let p = document.querySelector(".p2.p")
	console.log(p)

	//ppp p
	p.className = 'ppp p'

	// ppp p pppp
	// p.className = "ppp p pppp"
	p.className+=" pppp"
</script>
</body>
</html>